If $3a + b = 7$ and $6x + 4y = -8$, what is $-20y - 30x - 21a - 7b$ ?
$= -21a - 7b - 30x - 20y$ $= (-7) \cdot (3a + b) + (-5) \cdot (6x + 4y)$ $= (-7) \cdot (7) + (-5) \cdot (-8)$ $= -49 + 40$ $= -9$